Nano Tech Center

Projection Displays with High Power LEDs

R. Gale, H. Temkin, and J. Berg

Schematic diagram of a projection display system based on arrays of digital mirrors
known as DMD.

Projection displays based on large arrays of digital mirrors offer high image brightness
and resolution, as well as excellent color fidelity. The digital micromirrors themselves
are exceptionally robust, reliable, and energy efficient. In contrast, high brightness
lamps used in projection systems delivering well over 100 lumens on a screen are not
efficient or reliable and present difficult thermal management problems. In this context,
rapid development of high power light emitting diodes based on InGaN presents a possibility
of replacing conventional lamps and simplifying the image formation process, an interesting
challenge. Commercially available green (520 nm) and blue (480 nm) LEDs are now available
with power outputs in the 100 mW range. However, the emission pattern of these devices
and their thermal characteristics are poorly matched to the needs of projection systems.

Our research is focused first on understanding the limitations of current LED technology,
the manufacturers at the leading edge of development, and the rate of advance. While
evaluating currently available products, we are developing the optical systems required
to couple the the light efficiently into the continuously evolving DLP™ systems. We
are also evaluating reliabilty and lifetime issues in sequential pulsed operation,
and some of the advantages that accrue from the rapid switching capability of LED
illuminators. We have developed a detailed thermal model of high power LEDs and are
currrently verifying thermal management of multiple LEDs flip-chip mounted on a common
carrier.